The present invention relates to an image forming apparatus which forms an electrostatic latent image on an image carrier by using writing electrodes of a writing head, thereby forming the image.
In a conventional image forming apparatus such as an electrostatic copying machine and a printer, the surface of a photoreceptor is uniformly charged by a charging device and the uniformly charged surface of the photoreceptor is then exposed to light from an exposure device such as laser beam or LED light, whereby an electrostatic latent image is written on the surface of the photoreceptor. Then, the electrostatic latent image on the surface of the photoreceptor is developed by a developing device to form a developer image on the surface of the photoreceptor. The developer image is transferred to a recording medium such as a paper, thereby forming the image.
In such conventional image forming apparatus, the exposure device as a writing device for electrostatic latent image comprises a laser beam generating device or a LED light generating device. Therefore, the entire image forming apparatus should be large and complex.
Therefore, an image forming apparatus has been proposed in Japanese Patent Publication No. S63-45104 (hereinafter, ""104B publication) which employs electrodes, as a writing device for forming an electrostatic latent image, to write an electrostatic latent image on a surface of a image carrier without using any of laser beams and LED lights.
The image forming apparatus disclosed in the ""104B publication is provided with a multi-stylus having a large number of needle electrodes. The needle electrodes are just arranged in contact with an inorganic glass layer on the surface of the image carrier. In accordance with an input signal for image information, voltage is selectively applied to corresponding ones of the needle electrodes of the multi-stylus, whereby the electrostatic latent image can be formed on the image carrier. Since the image forming apparatus according to the ""104B publication does not use an exposure device conventionally used as a writing device, the invention of this publication makes it possible to provide an image forming apparatus which is relatively small in size and relatively simple in structure.
In addition, an image forming apparatus has been proposed in Japanese Unexamined Patent Publication No. H06-166206 (hereinafter, ""206A publication), comprising ion control electrodes which are disposed on a front end portion of an insulating substrate and are arranged in non-contact with an image carrier, wherein the ion control electrodes control ions generated by a corona discharger so as to write an electrostatic latent image on the image carrier. Since the image forming apparatus according to the ""206A publication also does not use an exposure device as a writing device, the invention of this publication makes it possible to provide an image forming apparatus which is relatively small in size and relatively simple in structure.
However, in the image forming apparatus according to the ""104B publication, the large number of needle electrodes of the multi-stylus are just arranged in contact with the inorganic glass layer on the surface of the image carrier. It is difficult to keep the stable contact between the needle electrodes and the inorganic glass layer on the surface of the image carrier. Accordingly, it is difficult to stably apply charge to the surface of the image carrier. This means that it is hard to obtain a high quality image.
Moreover, it is unavoidable to employ an inorganic glass layer on the surface of the image carrier for protecting the surface of the image carrier from damage due to contacts of the large number of needle electrodes. This makes the structure of the image carrier more complex. In addition, since the inorganic glass layer has quite well physical adsorbed water characteristic, moisture is easily adsorbed by the surface of the inorganic glass layer. Due to the moisture, the electrical conductivity of the glass surface is increased so that electrostatic charge on the image carrier should leak. Therefore, the image forming apparatus should be provided with a means for drying the surface of the image carrier with adsorbed moisture in order to prevent the apparatus from being affected by absorbed water. This not only makes the apparatus larger but also increases the number of parts, leading to problems of making the structure further complex and increasing the cost.
Since the large number of needle electrodes discharge, the apparatus has another problem that there is a high possibility of generation of ozone (O3). The presence of ozone may not only produce rusts on parts in the apparatus but also melt resin parts because ozone reacts with NOx to generate nitric acid (HNO3). Again ozone may give an offensive smell. Therefore, the image forming apparatus should be provided with a ventilation system including a duct and an ozone filter which sufficiently exhausts ozone from the inside of the apparatus. This also not only makes the apparatus larger but also increases the number of parts, leading to problems of making the structure further complex and increasing the cost.
On the other hand, in the image forming apparatus according to the ""206A publication, ions produced by the corona discharger are controlled by the ion control electrodes. This means that the apparatus is structured not to directly inject electric charge to the image carrier. The invention of the ""206A publication has problems of not only making the image forming apparatus larger and but also making the structure complex. Since the application of charge is conducted by ions, it is difficult to stably write an electrostatic latent image on the image carrier.
Further, since the generation of ions essentially generates ozone, there are problems similar to those described with regard to the image forming apparatus according to ""104B publication.
In order to solve the above problems, the applicant of this application filed a patent application to Japanese Patent Office (Japanese Patent Application No. 2001-227630, hereinafter ""630 application) proposing an image forming apparatus which makes it possible to reduce the size thereof and reduce the number of parts thereof so as to have more simple and low-priced structure, to more stably write an electrostatic latent image, and to inhibit the generation of ozone.
Since the details of the image forming apparatus proposed in the ""630 application will be easily understood by persons skilled in the art on consideration of the specification and drawings of the patent application, the details thereof will be omitted here. Only parts directly related to the present invention will be briefly described.
FIG. 1 is an illustration schematically showing the basic structure of the image forming apparatus proposed in the ""630 application.
As shown in FIG. 1, the image forming apparatus 1 comprises an image carrier 2 having a substrate 2a which is made of a conductive material such as aluminum and is grounded and a chargeable layer 2d which is formed on the outer periphery of the substrate 2a and has an insulating property and on which a electrostatic latent image is formed, a writing head 3 having a flexible substrate 3a, having high insulation property and being relatively soft and elastic, such as a FPC (Flexible Print Circuit: hereinafter, referred to as xe2x80x9cFPCxe2x80x9d) or a PET (polyethylene terephthalate: hereinafter, referred to as xe2x80x9cPETxe2x80x9d), and writing electrodes 3b which are supported by the substrate 3a and which are pressed lightly against the image carrier 2 with weak elastic restoring force created by deflection of the substrate 3a so that the writing electrodes 3b are in plane contact with the charged layer of the image carrier 2 to write the electrostatic latent image, a developing device 4 having a developer carrier (hereinafter, sometimes referred to as xe2x80x9cdevelopment rollerxe2x80x9d) 4a, and a transferring device 6 having a transfer roller 6a as a transfer member.
In the image forming apparatus 1 having a structure as mentioned above, after the chargeable layer 2b of the image carrier 2 is made into the uniformly charged state, writing voltage is applied to the writing electrodes 3b via IC drivers 7, and an electrostatic latent image is written on the chargeable layer 2b of the image carrier 2 mainly via the charge transfer (hereinafter, sometimes referred to as xe2x80x9ccontact-charge transferxe2x80x9d) between image carrier 2 and the writing electrodes 3b of the writing head 3 which are in plane contact with each other. The electrostatic latent image on the chargeable layer 2b of the image carrier 2 is then developed with developer carried by the development roller 4a of the developing device 4 to form a developer image and the developer image is transferred to the recording medium 5, such as a paper or an intermediate transfer medium, by the transfer roller 6a of the transferring device 6 to which transfer voltage is applied. Though the following description of the present invention will be made using paper as typical of the recording medium 5, it will be understood that media other than paper can be used as the recording medium 5.
In the writing process by the writing electrodes 3b of the writing head 3 as described above, in case of successively printing monochrome images, the transfer roller 6a is in contact with the chargeable layer 2b of the image carrier 2 after an image is printed on a paper 5 before the next paper 5 reaches the transferring device 6 as shown in FIG. 2. If the transfer voltage is continuously applied to the transfer roller 6a even during this, a potential corresponding to the transfer voltage is applied on the chargeable layer 2b of the image carrier 2. In this state, as the writing is conducted by the writing electrodes 3b, an electric current of high voltage exceeding the withstand voltage of the IC drivers 7 connected to the writing electrodes 3b is applied to the writing electrodes 3b, thus braking the writing head 3. Particularly, when the transfer voltage is increased in order to carry out the transfer in such an environment (LL environment) of low temperature (for example, 15xc2x0 C.) and low humidity (for example, 23% R.H.), the IC drivers 7 may be also broken.
If charge injection from the transfer roller 6a of the transferring device 6 onto the chargeable layer 2b of the image carrier 2, i.e. reverse charge injection, takes place, the rule of writing potentials in subsequent selective charging is disturbed, thus producing a ghost image and causing voltage drop due to discharge between the image carrier 2 and the writing electrodes 3b during the process of writing a latent image. Such voltage drop puts the electrostatic latent image into disorder.
If the writing electrodes 3b and the image carrier 2 are in contact with each other in the state where the reverse charge injection takes place at the transfer portion, an electric potential difference exceeding the discharge starting voltage is applied. Vibration may be produced due to the relation with the frequency of ON/OFF signals applied to the writing electrodes 3b for writing an electrostatic latent image. Such vibration enhances the instability in contact between the writing electrodes 3b and the image carrier 2 and loses stable reproducibility of latent images.
When the writing positions (that is, the contact positions of the writing electrodes 3b relative to the chargeable layer 2b) are shifted or the contact pressures of the writing electrodes 3b against the chargeable layer 2b vary during the process of writing an electrostatic latent image onto the chargeable layer 2b by the writing electrodes 3b of the writing head 3, the latent image and the developer image may be in disorder. In particular, the contact pressures between the writing electrodes 3b and the image carrier 2 are affected by the contact resistance during the charge transfer between the writing electrodes 3b and the image carrier 2, thus affecting the image forming speed (charge and discharge speed) and the image forming stability.
Therefore, it is desired to install the image carrier 2 and the writing electrodes 3b into the body frame of the image forming apparatus to define the writing positions of the writing electrodes 3b and the contact pressures of the writing electrodes 3b against the chargeable layer 2b as precise as possible, in order to obtain high quality images. It is also desired to facilitate such installation.
It is an object of the present invention to provide an image forming apparatus capable of preventing reverse charge injection from a transfer member to an image carrier at a transferring portion as completely as possible so as to obtain stable reproducibility of latent images and capable of controlling the potential of the image carrier to adjust the voltage of a writing head not to exceed the withstand voltage of the writing head so as to make it possible to protect IC drivers of writing electrodes even if the reverse charge injection from the transfer member to the image carrier occurs.
It is another object of the present invention to provide an image forming apparatus capable of more stably writing an electrostatic latent image and making it possible to precisely and easily set the writing positions and the contact pressure of writing electrodes.
It is still another object of the present invention to provide an image forming apparatus capable of obtaining stable reproducibility of latent images by preventing the occurrence of reverse charge injection from the transferring member to the image carrier when transfer is not conducted and yet achieving reduction in size and reduction in the number of parts thereof so as to have more simple and low-priced structure.
In order to achieve these objects, the present invention provides an image forming apparatus comprising at least: an image carrier having a chargeable layer on which an electrostatic latent image is formed; a writing head having writing electrodes which are in contact with said chargeable layer of said image carrier to write said electrostatic latent image; a developing device having a developer carrier for carrying developer for developing said electrostatic latent image on said image carrier; a transferring device having a transfer member which is disposed to be in contact with said chargeable layer of said image carrier to transfer the developer image, developed by the developing device, on said image carrier to a recording medium; and a surface potential adjusting member which is disposed to be in contact with said chargeable layer between said writing electrodes and said transfer member and to which a predetermined voltage including 0 (zero) V is applied for adjusting the voltage of said chargeable layer at the portion to be in contact with said writing electrodes.
The present invention is characterized in that said surface potential adjusting member rotates to have a predetermined peripheral surface speed ratio relative to said image carrier.
The present invention is characterized in that said surface potential adjusting member has a cleaning function.
The present invention is characterized in that said surface potential adjusting member is a rotatable conductive roller.
The present invention is characterized in that said conductive roller is any one of a group consisting of a conductive fur brush, a conductive rubber roller, and a conductive magnetic brush.
The present invention is characterized in that said predetermined voltage to be applied to said surface potential adjusting member is a voltage composed of an alternating current voltage superimposed on a direct current voltage.
The present invention is characterized in that the value of said direct current voltage is set to be equal to the value of a bias voltage to be applied to said image carrier.
The present invention is characterized in that the timing for conducting the application of voltages after the start of image forming is set such that the application of voltage to the surface potential adjusting member is first conducted for removing charge of said image carrier among the application of voltage to said image carrier, the application of voltage to said writing electrodes, the application of voltage to said developer carrier, the application of voltage to said transfer member, and the application of voltage to said surface potential adjusting member.
The present invention is characterized in that the timing for stopping the application of voltages after the finish of the image forming process is set such that the application of voltage to the surface potential adjusting member is last stopped for removing charge of said image carrier among the application of voltage to said image carrier, the application of voltage to said writing electrodes, the application of voltage to said developer carrier, the application of voltage to said transfer member, and the application of voltage to said surface potential adjusting member.
The present invention is characterized in that image carrier units each composed of said writing head, said developing device, said image carrier, and said surface potential adjusting member are provided for four colors of yellow, magenta, cyan, and black, respectively and that said image carrier units are disposed such that said image carriers thereof are in contact with an intermediate transfer medium and arranged sequentially along the moving direction of said intermediate transfer medium.
Further, the present invention also provides an image forming apparatus comprising at least: an image carrier on which an electrostatic latent image is formed; a writing head for writing said electrostatic latent image onto said image carrier by writing electrodes thereof; a developing device for developing said electrostatic latent image on said image carrier with developer; and a transferring device for transferring the developer image, developed by the developing device, on said image carrier, wherein said electrostatic latent image written on said image carrier by the writing electrodes of said writing head is developed by said developing device to form a developer image and the developer image on said image carrier is transferred by said transferring device, thereby forming an image, and wherein said writing head and said image carrier are positioned and fixed to a common frame.
The present invention is characterized in that said writing head, said image carrier, and said frame are structured as a cartridge.
The present invention is characterized in that at least one of said developing device and said transferring device is also positioned and fixed to said frame.
The present invention is characterized in that said writing head, said image carrier, at least one of said developing device and said transferring device, and said frame are structured as a cartridge.
The present invention further provides an image forming apparatus comprising at least: an image carrier on which an electrostatic latent image is formed; a writing head for writing said electrostatic latent image onto said image carrier by writing electrodes thereof; a developing device for developing said electrostatic latent image on said image carrier with developer; and a transferring device for transferring the developer image, developed by the developing device, on said image carrier, wherein said electrostatic latent image written on said image carrier by the writing electrodes of said writing head is developed by said developing device to form a developer image and the developer image on said image carrier is transferred by said transferring device, thereby forming an image and wherein said writing head and said image carrier are structured as a cartridge.
The present invention is characterized in that at least one of said developing device and said transferring device is also structured as another component of said cartridge.
The present invention provides an image forming apparatus comprising at least: image carriers which are provided for four colors of yellow, magenta, cyan, and black, respectively and on which electrostatic latent images of the corresponding colors are formed, respectively; writing heads which are provided to correspond to said image carriers for the four colors, respectively and each of which writes said electrostatic latent image of the corresponding color by writing electrodes thereof for the corresponding color; and developing devices which are provided to corresponding to said image carriers for the four colors, respectively and each of which develops said electrostatic latent image on said image carrier of the corresponding color with the corresponding color developer, wherein pairs of said image carriers and said writing heads, each pair being composed of the image carrier and the writing head for the same color, are arranged sequentially in tandem and wherein said image carrier and said writing head of each pair are positioned and fixed to a common frame.
The present invention further provides an image forming apparatus comprising at least: an image carrier having a chargeable layer on which an electrostatic latent image is formed; a writing head having writing electrodes which are in contact with said chargeable layer to write said electrostatic latent image; a developing device for developing said electrostatic latent image on said image carrier with developer; and a transferring device having a transfer member which comes in contact with said chargeable layer of said image carrier so that the developer image, developed by the developing device, on said image carrier is transferred to a recording medium; wherein the transfer voltage applied to said transfer member is set such that the transfer voltage when said transfer member is in contact with said image carrier never exceeds the maximum applied voltage to said writing electrodes.
The present invention furthermore provides an image forming apparatus comprising at least: an image carrier having a chargeable layer on which an electrostatic latent image is formed; a writing head having writing electrodes which are in contact with said chargeable layer to write said electrostatic latent image; a developing device for developing said electrostatic latent image on said image carrier with developer; an intermediate transfer medium which comes in contact with said chargeable layer of said image carrier so that the developer image, developed by the developing device, on said image carrier is transferred to said intermediate transfer medium; and a transferring device having a transfer member for transferring the developer image on said intermediate transfer medium to a recording medium; wherein the intermediate transfer voltage applied to said intermediate transfer member is set such that the intermediate transfer voltage when said intermediate transfer medium is in contact with said image carrier never exceeds the maximum applied voltage to said writing electrodes.
The present invention still further provides an image forming apparatus comprising at least: an image carrier having a chargeable layer on which an electrostatic latent image is formed; a writing head having writing electrodes which are in contact with said chargeable layer to write said electrostatic latent image; a developing device for developing said electrostatic latent image on said image carrier with developer; a transferring device having a transfer member which brings a recording medium into contact with said chargeable layer of said image carrier to transfer the developer image on said image carrier to said recording medium by transfer voltage applied to said transfer member; and a transfer member shifting mechanism which biases said transfer member against said chargeable layer to bring said recording medium into contact with said chargeable layer when said transfer voltage is applied and the operation of transferring the developer image on said image carrier to said recording medium is conducted and which separates said transfer member from said chargeable layer when the operation of transferring the developer image on said image carrier to said recording medium is not conducted.
The present invention is characterized by further comprising a surface potential adjusting member which is disposed to be in contact with said chargeable layer between said writing electrodes and said transfer member and to which a predetermined voltage including 0 (zero) V is applied for adjusting the voltage of said chargeable layer at the portion to be in contact with said writing electrodes.
The present invention provides an image forming apparatus comprising at least: an image carrier having a chargeable layer on which an electrostatic latent image is formed; a writing head having writing electrodes which are in contact with said chargeable layer to write said electrostatic latent image; a developing device for developing said electrostatic latent image on said image carrier with developer; an intermediate transfer medium which comes in contact with said chargeable layer of said image carrier so that the developer image, developed by the developing device, on said image carrier is primarily transferred to said intermediate transfer medium; and a primary transferring device having a primary transfer member which brings said intermediate transfer medium into contact with said chargeable layer of said image carrier to primarily transfer the developer image on said image carrier to said intermediate transfer medium by transfer voltage applied to said primary transfer member; and a transfer member shifting mechanism which biases said primary transfer member against said chargeable layer to bring said intermediate transfer medium into contact with said chargeable layer when said transfer voltage is applied and the operation of primarily transferring the developer image on said image carrier to said intermediate transfer medium is conducted and which separates said primary transfer member from said intermediate transfer medium when the operation of primarily transferring the developer image on said image carrier is not conducted.
The present invention is characterized by further comprising a surface potential adjusting member which is disposed to be in contact with said chargeable layer between said writing electrodes and said primary transfer member and to which a predetermined voltage including 0 (zero) V is applied for adjusting the voltage of said chargeable layer at the portion to be in contact with said writing electrodes.
The present invention provides an image forming apparatus comprising; image carrier units provided for four colors of yellow, magenta, cyan, and black, respectively, each of said image carrier unit being composed of an image carrier having a chargeable layer on which an electrostatic latent image is formed, a writing head having writing electrodes which are in contact with said chargeable layer to write said electrostatic latent image, and a developing device for developing said electrostatic latent image on said image carrier with developer, wherein said image carrier units for respective colors are disposed such that said image carriers thereof are in contact with an intermediate transfer medium and arranged sequentially along the moving direction of said intermediate transfer medium, and wherein said image forming apparatus further comprises primary transferring devices provided for the respective colors, each of said primary transferring device having a primary transfer member which brings said intermediate transfer medium into contact with said chargeable layer of the corresponding image carrier so that the developer image on said image carrier is primarily transferred to said intermediate transfer medium by transfer voltage applied to said primary transfer member, and transfer member shifting mechanisms provided for the respective colors, each of which biases said primary transfer member against said chargeable layer to bring said intermediate transfer medium into contact with said chargeable layer when said transfer voltage is applied and the operation of primarily transferring the developer image on said image carrier to said intermediate transfer medium is conducted and separates said primary transfer member from said chargeable layer when the operation of primarily transferring the developer image on said image carrier is not conducted.
The present invention is characterized by further comprising surface potential adjusting members provided for the respective colors, each of which is disposed to be in contact with said chargeable layer between said writing electrodes and said primary transfer member and to which a predetermined voltage including 0 (zero) V is applied for adjusting the voltage of said chargeable layer at the portion to be in contact with said writing electrodes.
In the image forming apparatus of the present invention structured as mentioned above, the surface potential adjusting member to which a predetermined voltage including 0 (zero) V is applied is disposed to be in contact with the chargeable layer between the writing electrodes and the transfer member and adjusts the voltage of said chargeable layer at the portion to be in contact with said writing electrodes. In the state that the transfer voltage is applied to the transfer member, when the transfer member is in contact with the chargeable layer of the image carrier during a period after the previous paper is sent off and before the next paper reaches or when the non-image area of the intermediate transfer medium comes in contact with the image carrier, reverse charge injection from the transfer roller onto the chargeable layer of the image carrier may occur. Even if the reverse charge injection occurs, the potential of the chargeable layer at its portion to be in contact with the writing electrodes is adjusted not to exceed the withstand voltage of the IC drivers of the writing electrodes by the surface potential adjusting member.
Therefore, this prevents the writing head from being broken, prevents the production of ghost image, and further inhibits voltage drop due to discharge between the image carrier and the writing electrodes during the process of writing a latent image, thereby preventing the electrostatic latent image from being in disorder.
Even when the transfer voltage is increased for conducting the transfer in the environment of low-temperature and low-humidity (LL), the IC drivers of the writing electrodes can be prevented from being broken.
Since the potential of the chargeable layer at the portion to be in contact with the writing electrodes is adjusted not to exceed the withstand voltage of the IC drivers, an electric potential difference exceeding the discharge starting voltage does not exist when the writing electrodes and the image carrier are in contact with each other. Production of vibration due to static electricity can be thus prevented in spite of the frequency of ON/OFF signals applied to the writing electrodes. Accordingly, the contact between the writing electrodes and the image carrier can be stabilized, thereby obtaining excellent reproducibility of latent images.
The surface potential adjusting member has a predetermined peripheral surface speed ratio relative to the image carrier, thus improving the potential adjustment of the chargeable layer. In addition, the surface potential adjusting member is composed of a rotatable conductive roller such as a conductive fur brush, a conductive rubber roller, or a conductive magnetic brush so as to increase the situation where the conductive roller is in contact with the image carrier, thereby further improving the potential adjustment of the chargeable layer. By designing the conductive roller to be in elastically contact with the image carrier, the contact ability is improved, further improving the potential adjustment of the chargeable layer of the image carrier.
Since the surface potential adjusting member has a cleaning function, the residual developer remaining on the image carrier after transfer can be removed by the surface potential adjusting member. If residual developer remains adhering to the image carrier and the peripheral surface speed ratio between the surface potential adjusting member and the image carrier is 1, the potential of the chargeable layer may be insufficiently adjusted. However, the residual developer on the image carrier can be surely removed because of the cleaning function, thereby ensuring the potential adjustment of the chargeable layer and preventing developer from adhering to the writing electrodes.
The surface potential adjusting bias voltage to be applied to the surface potential adjusting member is set to a voltage composed of an alternative current voltage having a suitable frequency superimposed on a direct current set as a reference voltage (for example, ground reference voltage) to be applied to the image carrier, thereby efficiently collecting negatively charged residual developer remaining on the image carrier after transfer and securely adjusting the surface potential of the chargeable layer of the image carrier to the reference bias voltage (for example, the ground reference voltage).
Since the timing for conducting the application of voltages after the start of image forming is set such that the application of voltage to the surface potential adjusting member is first conducted for removing charge of said image carrier among the application of voltage to said image carrier, the application of voltage to said writing electrodes, the application of voltage to said developer carrier, the application of voltage to said transfer member, and the application of voltage to said surface potential adjusting member, the surface potential of the chargeable layer of the image carrier can be securely adjusted to the reference bias voltage (for example, ground reference voltage).
On the other hand, since the timing for stopping the application of voltages after the finish of the image forming process is set such that the application of voltage to the surface potential adjusting member is last stopped for removing charge of said image carrier among the application of voltage to said image carrier, the application of voltage to said writing electrodes, the application of voltage to said developer carrier, the application of voltage to said transfer member, and the application of voltage to said surface potential adjusting member, whereby the surface potential of the chargeable layer of the image carrier can be securely adjusted to the reference bias voltage (for example, ground reference voltage).
The writing head and the image carrier are positioned and fixed to the common frame, thereby making it possible to precisely set the writing position of the writing electrodes of the writing head relative to the image carrier and making the contact pressure of the writing electrodes to the image carrier constant. Therefore, this prevents the latent image and its developer image from being in disorder. In addition, since the contact pressure of the writing electrodes to the image carrier is made constant, the charging and discharging speed i.e. the latent image forming speed can be stabilized and the latent image forming stability is improved. Accordingly, stable high-quality images can be obtained.
Since the writing head and the image carrier are previously fixed to the common frame, it is not necessary to align the writing electrodes with the image carrier and to adjust the contact pressure when installed to the body frame of the image forming apparatus, thereby easily and precisely mounting the writing head and the image carrier to the predetermined position of the body frame of the image forming apparatus.
Since the writing electrodes are in plain contact with the image carrier, the application of charge can be dominated by the charge-transfer between the writing electrodes and the latent image carrier which are in contact with each other and the charge-transfer can be stably and reliably conducted. The charge-transfer makes it possible to stably and easily write electrostatic latent image on the image carrier.
The image carrier, the writing head, at least one of the developing device and the transferring device are positioned and fixed to the common frame, thereby still further precisely conducting the formation of images and providing higher quality images.
The image carrier, the writing head, and the frame, or the image carrier, the writing head, at least one of the developing device and the transferring device, and the frame are structured as a cartridge, thus significantly facilitating the installation and the replacement of the writing head and the image carrier relative to the body frame of the image forming apparatus.
Since the image carrier and the writing head, or the image carrier, the writing head, at least one of the developing device and the transferring device are structured as a cartridge, the necessity of the flame can be eliminated, thus reducing the number of parts and further facilitating the attachment or exchange of these relative to the body frame of the image forming apparatus.
The writing head and the image carrier of each pair for each color of yellow, magenta, cyan, or black are fixed to the corresponding frame not to shift the relative position thereof, thereby making it possible to precisely set the writing positions of latent images to be written by the writing electrodes for the respective colors. This makes it possible to precisely tone the colors and position the latent images so as to provide high-quality full-color images.
Since the writing heads and the image carriers for the respective colors are previously fixed to the common frame, it is not necessary to align the writing electrodes of the writing heads with the image carriers when the frame is installed to the body frame of the image forming apparatus, thereby easily and precisely mounting the writing heads and the image carriers to the predetermined positions of the body frame of the full-color image forming apparatus.
In the state that the transfer voltage is continuously applied to the transfer member, the transfer member is in contact with the chargeable layer of the image carrier during a period after the previous paper is sent off before the next paper reaches and the non-image area of the intermediate transfer medium comes in contact with the image carrier. Since both the transfer voltage to be applied to the writing electrodes and the intermediate transfer voltage to be applied to the intermediate transfer medium are set to be equal to or lower than the maximum voltage to be applied to the writing electrodes, reverse charge injection from the transfer member or the intermediate transfer medium onto the image carrier never occurs. Therefore, the current flowing to the writing electrodes never exceed the withstand voltage of the high-voltage IC drivers connected to the writing electrodes. Therefore, similarly to the aforementioned case, this prevents the writing head from being broken, prevents the production of ghost image, and further inhibits voltage drop due to discharge between the image carrier and the writing electrodes during the process of writing a latent image, thereby preventing the electrostatic latent image from being in disorder. Even when the transfer voltage is increased for conducting the transfer in the environment of low-temperature and low-humidity (LL), the IC drivers of the writing electrodes can be prevented from being broken.
Since the reverse charge injection never occurs at the transfer portion, an electric potential difference exceeding the discharge starting voltage does not exist when the writing electrodes and the image carrier are in contact with each other. Production of vibration of the writing electrodes can be therefore prevented in spite of the frequency of ON/OFF signals applied to the writing electrodes. Accordingly, the contact between the writing electrodes and the image carrier can be stabilized, thereby obtaining excellent reproducibility of latent images.
The transfer member shifting mechanism biases the transfer member against said chargeable layer to bring the recording medium or the intermediate transfer medium into contact with the chargeable layer when the operation of transferring the developer image on the image carrier to the recording medium or the intermediate transfer medium is conducted. On the other hand, the transfer member shifting mechanism separates the transfer member from the chargeable layer of the image carrier or the intermediate transfer medium when the operation of transferring the developer image on the image carrier to the recording medium or the intermediate transfer medium is not conducted. That is, when neither a recording medium such as a paper nor a non-image area of the intermediate transfer medium exists between the image carrier and the transfer member, that is, when transfer operation is not conducted before the start of the transfer operation, after the finish of the transfer operation, or in an interval between the printed recording medium and the next recording medium in case of successively printing images on a predetermined number of recording media, the transfer member can be spaced apart from the chargeable layer of the image carrier or the intermediate transfer medium.
Therefore, the reverse charge injection from the non-image area of the transfer member or the intermediate transfer medium to the image carrier never occurs when operation of transferring the developer image on the image carrier to the recording medium or the intermediate transfer medium is not conducted and the current exceeding the withstand voltage of the IC drivers never flows to the writing electrodes, thereby preventing the writing head from being broken, prevents the production of ghost image, and further inhibits voltage drop due to discharge between the image carrier and the writing electrodes during the process of writing a latent image so as to prevent the electrostatic latent image from being in disorder. Even when the transfer voltage is increased for conducting the transfer in the environment of low-temperature and low-humidity (LL), the IC drivers of the writing electrodes can be prevented from being broken.
Since the reverse charge injection never occurs at the transfer portion, an electric potential difference exceeding the discharge starting voltage does not exist when the writing electrodes and the image carrier are in contact with each other. Production of vibration of the writing electrodes due to static electricity can be therefore prevented in spite of the frequency of ON/OFF signals applied to the writing electrodes. Accordingly, the contact between the writing electrodes and the image carrier can be stabilized, thereby obtaining excellent reproducibility of latent images.
Further, the surface potential adjusting member to which a predetermined voltage including 0 (zero) V is applied is disposed to be in contact with the chargeable layer between the writing electrodes and the transfer member and adjusts the voltage of said chargeable layer at the portion to be in contact with said writing electrodes similarly to the aforementioned case. By the surface potential adjusting member, the potential of the chargeable layer at the portion to be in contact with the writing electrodes is further reliably adjusted not to exceed the withstand voltage of the IC drivers of the writing electrodes.
Since the potential of the chargeable layer at the portion to be in contact with the writing electrodes never exceeds the withstand voltage of the IC drivers, an electric potential difference exceeding the discharge starting voltage does not exist when the writing electrodes and the image carrier are in contact with each other. Similarly to the above case, production of vibration of the writing electrodes can be therefore securely prevented.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.